This invention relates to a method and system for implementing a tactile virtual reality environment, and a six-axis manipulator with force feedback defining an interface device therefor.
In many applications it is desirable for a user to remotely control the operation of a slave device by means of a hand-controllerxe2x80x94a device which senses the movement of a handle gripped by the user""s hand and generates one or more control signals which, in turn, are used in directing the actuation of the slave device. Hand controllers are commonly used in applications where the user is necessarily in a location which is remote from the slave, for example, where the slave is in a hazardous environment, such as an environment where high levels of radiation are present. Hand controllers are also well suited for teleoperation in environments where direct viewing is limited. Examples include murky underwater environments with reduced light and obstructions such as underground excavation applications. To improve the sensitivity of the user to the slave""s environment, a force-feedback system can be used to reflect the forces generated on the hand back to the user via the hand controller. For instance, if the slave unit impacts an object, the force of the impact is felt by the user""s hand.
Force reflecting hand controllers for tele-operation are well known. Units which reflect the force sensed by a remote manipulator are.disclosed in U.S. Pat. Nos. 4,837,734 to Ichikawa et al., 4,853,874 to Iwamoto et al., 4,888,538 to Dimitrov et al., 4,893,981 and 5,018,922 to Yoshinada et al., 4,942,538 to Yuan et al., 5,004,391 to Burdea, and 5,053,975 to Tsuchihashi et al. These units use electrical force feedback, usually applied through an electric motor/gear drive, to present the forces sensed by a remote manipulator to the user.
FIG. 1 summarizes the basic operation of prior art devices. The position, velocity, and/or acceleration provided on a master hand controller 10 on a handle 12 by a user (not shown) is sensed and transmitted as a command by a controller 14 to move the slave device 16. .In turn, the actual position, velocity, and/or acceleration is read from the slave device 16 and is sent back by the controller 14 as a command to the master hand controller 10, providing the user with direct kinesthetic feedback from the remote device he is controlling.
To simplify control, many prior art devices are a kinematically similar replica of the remote device under control. This kinematic similarity reduces or eliminates the need for a computer controlled interface between the master hand controller unit and the remote slave device. This kinematic similarity requires a unique hand-controller for each unique slave device. Changes made to the kinematics of the slave device require similar changes to the controller.
Prior force reflecting hand controller configurations have used either counter weights or active compensation to remove friction and gravity effects from the controller handle. The use of counterweights increases the mass and moment of inertia of the system which, in turn, increases user reaction time due to the additional forces necessary to accelerate and decelerate the handle. Active gravity compensation increases the complexity of a system while simultaneously increasing the possibility of undesirable system instability.
Further, by reacting to remote forces present on a slave device, the prior art devices lack the capability of creating a three-dimensional tactile virtual reality environment whereby a user""s actions and reactions are related to a simulated world such simulations of driving or flying functions, simulation of molecular force interactions, or simulations of surgical procedures. U.S. Pat. No. 5,044,956 to Behensky et al. discloses a system whereby a steering wheel is used to input positions to a simulation which in turns actuates the wheel in response to simulated artifacts. This system does not disclose or anticipate the simulation and coordination of the six-degrees of freedom required for the arbitrary positioning and orientation of solid objects. Similarly, prior art devices which simulate virtual reality by visual feedback to a user are not capable of accepting tactile inputs and providing tactile force feedback.
The present invention solves the problems of the prior art by providing a method and system for providing a tactile virtual reality in response to user position and orientation. The present invention further provides a universal device whose kinematics do not replicate any particular device it might control or simulate. A computer mediated control system is provided which transforms forces, torques, displacements, velocities, and accelerations measured by a simulated environment and applies them hand controller or vice versa. The present invention can effect and control the superposition of translational displacement with force application and angular displacement with torque, thus providing arbitrary, programmed application of forces, torques, and displacements to the user in any direction. This allows the device to be controlled by, and to control, external simulations or models as well as physical remote devices. The invention can also locally simulate virtual force fields generated from interaction with virtual surfaces and/or boundaries, can provide software programmed position, velocity, force, and acceleration limit stops, and can dynamically shift, rotate, or scale these virtual objects.
The present invention includes a manipulator for use as a user interface which has a specific joint configuration. This joint configuration yields a design which passively solves the problem of gravity compensation by two constant force springs. Friction in the manipulator is minimized through using a highly back-drivable low gear ratio drive system and high performance brushless DC motors. A general object of the present invention is to provide a tactile virtual reality in response to a user input. According to the present invention, an electric signal is generated for each of a plurality of degrees of freedom of the user as a function of the user position and orientation in three-dimensional space. At least one virtual reality force field is generated in response to the generated signals. A fourth signal is generated for each degree of freedom as a function of the force field, and a tactile force on the user is generated for each force. signal.
A further general object of the present invention is to provide a system for providing a tactile virtual reality in response to a user input. The system comprises a six-axis interface device having an actuator for each axis and a member movable by the user. The interface device is responsive to the position and orientation of the member to generate electrical signals representative of this position and orientation. Means are also provided f or generating at least one virtual reality force field responsive to the electric signals. In addition, means for generating a force signal for each axis are provided as a function of the force field wherein the actuators are responsive to their respective force signals to provide a force to each axis for creating the tactile virtual reality.
A specific object of the present invention is to provide a six-axis manipulator capable of assuming an arbitrary orientation and position in three-dimensional space for use as a user interface.
A further specific object of the present invention is to provide a six-axis manipulator for use as a user interface having a constant force spring for compensating for the force of gravity.